Chapter 16, Problem 62A

(a)

Interpretation Introduction

Interpretation: The percent by mass of $\text{NaCl}$ is to be calculated when $44\text{ g}$ $\text{NaCl}$ dissolved in $756\text{ g}$ ${\text{H}}_2\text{O}$ .

Concept Introduction: Mass percent is the relative amount of one element or solute in the solution. In terms of mass, it is shown as $\text{(w/w)\%}$ .

The expression for mass percent is as follows:

  $masspercent=\frac{\text{mass of solute}}{Totalmass}\times 100$

Answer to Problem 62A

The mass percent of $\text{NaCl}$ is $5.5\%$ .

Explanation of Solution

Given,

Mass of $\text{NaCl}$ is $44\text{ g}$ .

Mass of ${\text{H}}_2\text{O}$ is $756\text{ g}$ .

The total mass is calculated as:

  $\begin{array}{c}Totalmass=44\text{ g}+756\text{ g}\\ =800\text{ g}\end{array}$

Substitute, $44\text{ g}$ for the mass of solute and $800g$ for the total mass in the expression for mass percent.

  $\begin{array}{c}masspercent\text{of NaCl}=\frac{44}{800}\times 100\\ =5.5\%\end{array}$

The mass percent of $\text{NaCl}$ is $5.5\%$ .

(b)

Interpretation Introduction

Interpretation: The percent by mass of $\text{NaCl}$ is to be calculated when $15\text{ g}$ $\text{NaCl}$ dissolved in $485\text{ g}$ ${\text{H}}_2\text{O}$ .

Concept Introduction: Mass percent is the relative amount of one element or solute in the solution. In terms of mass, it is shown as $\text{(w/w)\%}$ .

Answer to Problem 62A

The mass percent of $\text{NaCl}$ is $3.0\%$ .

Explanation of Solution

Given, Mass of $\text{NaCl}$ is $15\text{ g}$ .

Mass of ${\text{H}}_2\text{O}$ is $485\text{ g}$ .

The total mass is calculated as:

  $\begin{array}{c}Totalmass=15\text{ g}+485\text{ g}\\ =500\text{ g}\end{array}$

Substitute $15\text{ g}$ for the mass of solute and $500g$ for the total mass in the expression for mass percent.

  $\begin{array}{c}masspercent\text{of NaCl}=\frac{15}{500}\times 100\\ =3.0\%\end{array}$

The mass percent of $\text{NaCl}$ is $3.0\%$ .

(c)

Interpretation Introduction

Interpretation: The percent by mass of $\text{NaCl}$ is to be calculated when $135\text{ g}$ $\text{NaCl}$ dissolved in $765\text{ g}$ ${\text{H}}_2\text{O}$ .

Concept Introduction: Mass percent is the relative amount of one element or solute in the solution. In terms of mass, it is shown as $\text{(w/w)\%}$ .

Answer to Problem 62A

The mass percent of $\text{NaCl}$ is $15.1\%$ .

Explanation of Solution

Given, Mass of $\text{NaCl}$ is $135\text{ g}$ .

Mass of ${\text{H}}_2\text{O}$ is $756\text{ g}$ .

The total mass is calculated as:

  $\begin{array}{c}Totalmass=135\text{ g}+756\text{ g}\\ =891\text{ g}\end{array}$

Substitute, $135\text{ g}$ for the mass of solute and $891g$ for the total mass in the expression for mass percent.

  $\begin{array}{c}masspercent\text{of NaCl}=\frac{135}{891}\times 100\\ =15.1\%\end{array}$

The mass percent of $\text{NaCl}$ is $15.1\%$ .